At 1509 GMT shares stood at 368.25 pence, down 8.22% from Thursday's close of 401.25 pence. Shell said that the reduction in its proved reserve base would not have any impact on its financial performance, or on the amount of hydrocarbons it ultimately expected to recover from its portfolio. Simon Henry, Shell's head of investor relations, told a conference call that the cut in proved reserves followed a reassessment of which reserves the company had "reasonable confidence" in as being proven.

Around 90% of the total being removed from the proved category are currently undeveloped, with a little under 10% from producing assets. "We identified it and we are facing it. There is no material impact on our financials," said Henry. In the long run, Shell still expects that most of the reserves affected will be re-booked in the proved category as developments move forward. Around 50% of the downward revision relates to onshore discoveries in Nigeria and assets in Australia, notably the Gorgon LNG project. The remaining cut in proved reserves estimates are spread between several other countries, with no single one accounting for more than 10% of the total, Henry said.

Shell had booked reserves from Gorgon as proved even though the project has not yet received final approval from its partners. Shell has not yet determined how much of the 3.9-bil boe being downgraded will move to 'probable' reserve status and how much to the more distant 'discovered scope for recovery' category.

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